Process for unhairing of hides



United States Patent Office 2,791 ,535 Patented May 7, 1957 PROCESS FOR UNHAIRING F HIDES Theone C. Cordon, Philadelphia, Pa., assignor to the United States of America as represented by the Secrctary of Agriculture No Drawing. Application August 4, 1955, Serial No. 526,578

3 Claims. (Cl. 195-6) (Granted under Title 35, U. S. Code (1952), see. 266) A non-exclusive, irrevocable, royalty-free license in the invention herein described, for all governmental purposes, throughout the world, with power to grant sublicenses for such purposes, is hereby granted to the Government of the United States of America.

The enzymatic unhairing of hides is of ancient origin. The enzymes so used, if identified, have practically always been of proteolytic nature. Recently, Burton et. al., I. S. L. T. C., 37, 82 (1953), have claimed that so-called mucolytic enzymes, including amylases, removed the hair from calfskin in 3 days. In a later report, however, Gillespie, ibid., 344, tested a variety of amylases and found no unhairing activity. He attributed Burtons observations to contaminating bacteria.

Because amylases are among the more abundant, easily produced and inexpensive commercial enzymes, it is the object of this invention to provide practical processes for the unhairing of hides by use of amylases. By hides we mean all animal skins that are commonly unhaired for the production of leather, the more important examples being cowhide, calfskin, sheepskin, goatskiu or horsehide.

We have found that when fresh hide is treated with any of the various commercial amylases for several days, the unhairing action, if any, is variable, uncertain and incomplete, and hence, is of no practical value. Quite unexpectedly, however, We have found that if the hide is treated with common salt before or during the amylase treatment, the unhairing action of the amylase is greatly intensified, so that complete unhairing is achieved within about 1-3 days.

Most hides are conventionally preserved by salting with dry salt. This salt treatment is sufiicient to make possible amylase unhairing of the hide. Alternatively, fresh hides may be treated with concentrated, or even saturated, brine to activate the enzyme action. It is a surprising fact, however, that the optimum salt treatment consists of soaking the hide in a relatively dilute brine of about 2 to 3% concentration.

While the salt and the amylase may be applied simultaneously in a single solution, we have found that the enzyme unhairing action is faster and more efiicient if the hide has been treated with salt before being treated with the enzyme. Thus, an effective procedure is to soak the hide in 2 to 3% brine for about 24 hours before adding the enzyme. The latter may then be added directly to the brine or it may be prepared as a separate solution into which the brined hide is transferred.

Like most chemical reactions, the unhairing action of the enzyme is accelerated by elevation of the temperature. Thus, an amylase preparation that requires 6 days for completely unhairing hides at 20 C. may do the same in 3 days at 38 or in 2 days at 45". While most amylases are stable to heat up to at least 50, hide is denatured to some extent if heated above about 45 C. for several hours. Consequently, we prefer to operate at temperatures below that point.

Commercial amylases vary widely in origin and potency but we have not found any that lack unhairing activity.

Since the unhairing action undoubtedly requires that the enzyme penetrate the hide to some extent, it is accelerated by agitation of the enzyme solution and/ or flexing of the hide during the enzyme treatment. Optimum results are obtained by carrying out the treatment in a rotating drum or other apparatus wherein the solution is agitated and the hide is tumbled or otherwise flexed.

In order to prevent possible microbial contamination and deterioration of the hide during the unhairing process, it is usually advisable to add a suitable antiseptic to the amylase solution to be used. A convenient one is phenylmercuric acetate used at a level of about 0.015%. This is ample to maintain sterility for at least 3 to 4 days.

The following experiment illustrates one satisfactory manner of practicing the invention:

Fresh cowhide was soaked overnight in 2% aqueous NaCl solution containing 0.015% of phenylmercuric ace tate. Then 0.25% by weight, based on the brine used, of an amylase preparation, was added. This amylase preparation had an assay value of mg. of maltose per mg. of enzyme preparation. The hide and treating solution were then agitated by rotation at 10 R. P. M. in a square bottle while being maintained at 38 C. After 48 hours most of the hair had been loosened and after 72 hours the unhairing was complete.

When the above experiment was repeated, except that the brine treatment was omitted, only very slight, spotty unhairing was noted at 72 hours. When the brine and enzyme were added simultaneously, about 1 day more was required for complete unhairing. When agitation was omitted no unhairing was observed at 48 hours and it was incomplete at 72 hours. When the hide, in the form of 1" x 3" strips, was mechanically flexed 88 times per minute during the brine-enzyme treatment some unhairing was observed at 24 hours and it was complete in less than 72 hours.

Commercial salted hide required only about one-half as long for the amylase treatment to completely unhair it as did fresh hide. Moreover, the preliminary brine treatment could be omitted without affecting the amylase activity, since the hide already carried ample salt on and in it.

The word brine, as used herein, means an aqueous solution of sodium chloride.

I claim:

1. A process comprising treating a hide with an aqueous solution containing sodium chloride and amylase to unhair it.

2. A process comprising treating a hide with an aqeous solution containing sodium chloride and thereafter mixing amylase with the said sodium chloride solution and continuing the treatment of the hide with the resulting mixture to unhair it.

3. The process of claim 1 wherein the concentration of the sodium chloride in the solution is about from 2 to 3%.

References Cited in the file of this patent UNITED STATES PATENTS 427,779 Manwaring May 13, 1890 1,985,267 Wallerstein Dec. 25, 1934 2,599,867 Schubert June 10, 1952 2,607,359 Oesting Aug. 19, 1952 OTHER REFERENCES Tauber: Chemistry and Technology of Enzymes, John Wiley & Sons, Inc., 1949, pages 396 to 406. 

1. A PROCESS COMPRISING TREATING A HIDE WITH AN AQUEOUS SOLUTION CONTAINING SODIUM CHLORIDE AND AMYLASE TO UNHAIR IT. 